(i) Technical Field
The present invention relates to focal plane shutters and optical apparatuses.
(ii) Related Art
Japanese Unexamined Patent Application Publication No. 2009-122557 discloses an optical apparatus employing a focal plane shutter. The focal plane shutter is equipped with a board including an opening; blades opening and closing the opening; and a drive lever rotatably supported by the board and driving the blades.
The drive lever is biased by a drive spring, and rotated from a start end to a terminal end of a swingable range by a biasing force of the drive spring. The drive lever abuts an end portion of an escape slot provided in the board, and then stops at the terminal end of the swingable range. At this time, an impact is applied to the whole focal plane shutter. Therefore, the load applied to the drive lever or the whole focal plane shutter is a factor that reduces the reliability of performance of the focal plane shutter for long-term use. Further, the biasing force of the drive spring tends to increase in accordance with an increase in the speed of the focal plane shutter. Therefore, besides the above mentioned impact, there is a problem of an increase in the consumption current resulting from an increase in an amount of current in an electromagnet for holding the drive lever at a given position.